Bio 2 Ch 6

Bio 2 Ch 6

Metabolism: Energy and Enzymes

Cells and the flow of energy

Forms of energy

• All life requires energy to maintain structural organization and carry out metabolic activities.

• Energy - the ability to do work or to bring about a change.

• Kinetic energy is the energy of motion

• Mechanical energy is a type of kinetic energy

• Potential energy is stored energy that is not doing work at the moment

• Food is a form of potential energy called chemical energy because it is composed of organic molecules.

Two laws of thermodynamics

• The First Law of Thermodynamics states that energy cannot be created or destroyed, but it can be changed from one form to another.

• The Second Law of Thermodynamics states that energy cannot be changed from one form to another without a loss of usable/free energy

Cells and entropy

• According to the Second Law of Thermodynamics, with every energy transformation the universe becomes less organized and more disordered.

• The term entropy indicates the relative amount of disorganization

• All organisms depend on a constant supply of free energy to maintain the order of their metabolic processes required for sustaining life.

Metabolic Reactions and Energy

ATP: energy for cells

• All living organisms maintain their structure and function through chemical reactions

• --Metabolism is the sum of all the chemical reactions that occur in a cell

• --Reactants are substances that participate in a reaction

• --Products are substances that form as a result of a reaction

ATP (adenosine triphosphate)

• common energy currency of cells

• Cells do not store large amounts of ATP for use

• Instead they constantly regenerate ATP using ADP (adenosine diphosphate) and inorganic phosphate in a process called the ATP cycle

The ATP Cycle

• Each ATP molecule contains a nucleotide of the nitrogen containing base adenine and a 5 carbon sugar ribose and three phosphate groups

• ATP is broken down by hydrolysis, which releases stored energy.

The ATP Cycle

• ATP provides energy for coupled reactions and to change the shape of the reactant

• ATP supplies the energy needed to synthesize macromolecules, transport substances across the plasma membrane and permit movement chromosomes, cilia, muscles, and more

Metabolic pathways and enzymes

Enzyme-substrate complex

• Many chemical reactions in cells will occur spontaneously, but slowly

• An enzyme protein acts as a catalyst to speed up a chemical reaction by lowering the activation energy barrier

• The active site of an enzyme associates directly with the substrate

• Enzymes are specific to the reactions they catalyze because the active site is specifically shaped for their substrates

Induced fit model

• The induced fit model states that when a substrate is present in the active site, the enzyme will undergo a slight change in shape to accommodate the substrates to achieve optimum fit

• After the reaction, the product or products are released and the enzyme returns to its original state

Energy of activation

• The energy of activation is the initial investment of energy required for substrates to reach an unstable state where chemical bonds can break

• Adding an enzyme lowers the amount of activation energy needed to start the reaction

Factors affecting enzymatic speed

• Enzyme activity increases as substrate concentration increases. Maximum rate is reached when all active sites are filled with substrate

• Each enzyme has an optimal pH where it can maintain its normal structure and function

• A change in pH can cause the enzyme to denature (when an enzyme shape is altered in such a way that its active site can no longer interact with its substrates)

Factors affecting enzymatic speed

• As temperature rises, enzyme activity increases due to more frequent collisions between enzyme and substrate

• If temperature rises beyond a certain point, however, enzyme activity slows, then declines rapidly due to denaturing

• Many enzymes require the presence of an inorganic ion called cofactors to work

• Non-protein organic molecules called coenzymes also can participate in the reaction and may even accept or contribute atoms

Factors affecting enzymatic speed

• Vitamins are relatively small, organic molecules that are often components of coenzymes

• If vitamins are not available in our diets, enzyme activity will decrease

Enzyme inhibition

• Enzyme inhibition occurs when a molecule (the inhibitor) binds to an enzyme and decreases its activity

• Noncompetitive enzyme inhibition: The inhibitor binds to the enzyme at a location other than the active site (an allosteric site).

• This changes the shape of the enzyme, which in turn changes its function

Enzyme inhibition

• The inhibitor and the substrate compete for the active site of an enzyme

•  Normally, this is reversible and the enzyme can be used again.

• Irreversible inhibition occurs when an inhibitor permanently inactivates or destroys an enzyme

Oxidation-reduction reactions and metabolism

Oxidation-reduction reactions:

• In metabolic reactions, oxidation represented the loss of electrons, and reduction is the gain of electrons.

Chloroplasts and photosynthesis

• Chloroplast in plants capture solar energy and use it to convert water and carbon dioxide into a carbohydrate, releasing oxygen as a by product

• During photosynthesis, carbon dioxide is reduced and water is oxidized

Mitochondria and cellular respiration

• Present in both plants and animals, mitochondria oxidize carbohydrates and use the released energy to synthesize ATP molecules consuming oxygen in the process

• During cellular respiration, glucose is oxidized and oxygen is reduced